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Chemogeny or Chemical Origin of Life (Abiotic Synthesis of Macromolecules)About 4 billion years ago, earth's atmosphere had ammonia, methane and water vapours. There was no free oxygen. Formation of various simple and complex organic molecules from these gases involved following steps:Formation of Simple Organic Compounds: The primitive inorganic molecules interacted and combined to form simple organic compounds like alcohols, aldehydes, glycerol, fatty, acids, amino acids, sugars and nitrogenous bases.Formation of Complex Organic Compounds: Simple organic molecules underwent condensation, polymerisation and chance chemical reactions forming new and complex organic macromolecules such as polysaccharides, fats, proteins, nitrogenous bases, nucleosides and nucleotides.

In living organisms, biological reactions are sped up by enzymes, but in primitive sea, these enzymes were absent. So such reactions occurred far more slowly. Therefore, nature could synthesise all the compounds known to exist in the present day living beings but at a very slow pace.